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Chapter 5
Heredity
Heredity
The
passing of traits
from parents to
offspring.
Dominant Trait
 The
trait observed when
at least one dominant
allele for a characteristic
is inherited.
 Expressed by capitals
Recessive Trait
A
trait that is apparent only
when two recessive alleles
for the same characteristic
are inherited.
 Expressed in lowercase
Genes
 Segments
of DNA that
carry hereditary
instructions and are
passed from parent to
offspring: located on
chromosomes.
Alleles
 Different
forms of a
single gene.
 Example: hair color has
blonde, red, brown or
black alleles
Genotype
 The
inherited
combination of alleles.
 RR Rr or rr
 Heterozygous – Rr
 Homozygous – RR or rr
Phenotype
 An
organism’s inherited
appearance.
 Hair or eye color
Probability
 The
mathematical chance
that an event will occur.
 Expressed in fractions or
ratios
Gregor Mendel
 Born
in 1822
 Background in cultivating
flowers and fruit trees
 Studied patterns of
inheritance
Pea Plants
 Mendel
used
only pea
plants to
simplify his
investigation
Why use pea plants?
 Quick
growing
 Self
pollinating
 Many
varieties
available
Self Pollinating
 Contains
both male and
female reproductive
structures
 Male – anthers
 Female - stigma
How does pollination occur?
Characteristics of pea
plants
 Seed
Shape
 Plant
Height
–Round or wrinkled
–Tall or short
 Flower
Color
–Purple or white
True-breeding Plant
 When
a true breeding
plant self pollinates, it will
always produce offspring
with the same trait
Cross-pollination
 Remove
the anthers from
one plant so that it cannot
self pollinate
 Mendel could control the
pollination of the pea plants